Mata was denied by United keeper David de Gea late in the piece, with the Spanish gloveman also denying Oscar on a couple occasions, and his performance was not lost on his countryman.
The Chelsea midfielder was also quick to praise his own teammates for the way they responded when trailing by two goals.
"We were playing in a stadium like Old Trafford and it was Man United, so it could be a good result," Mata told ITV1.
"But in the second half we had so many chances to score. De Gea was good, saving some of them.
"He saved very well (from me), with a foot I think, and Oscar had so many chances.
"It's a day to be proud of the team. (United) scored two in the first minutes but we tried very hard and came back.
"We have a replay at home, we are strong at Stamford Bridge with our supporters, and we will try to get through."